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Fast sync box
THE FAST SYNC BOX: '''The fast sync box is a piece of homemade electronics that is used to correlate events in the lab to electron events. It is of high quality (Adriane) construction. Delay lines are made from passive delays that have super low temperature drift. In short, it is made to optimize correlation of external events with the ORTEC 9353 with minimal possible phase (timing) noise. The fast sync box is shown in the picture below. It’s insides are beautiful, and its outsides were done in a mad dash to get data before DAMOP 2011. Somebody should take the time to clean it up: The LEFT INPUT should be from '''either the left (looking down the beam line in the direction the beam travels) TTL output from the 9327 timing discriminating amp, o'''r the e- OUT of the voltage to random frequency converter. The RIGHT INPUT should be '''either the TTL output of the 9327 timing discriminating amp that is attached to the right anode 'o'r the I+ OUT of the voltage to random frequency converter. The switch in the middle of the front panel can be used to select if the left detector corresponds to electrons, or the right detector corresponds to electrons. This is accomplished through a logic gates that effectively switch the cabling. When using the voltage to random frequency converter to make faux ions, always use the L/e selection. If the switch is in the center position, then whether the LEFT INPUT or RIGHT INPUT corresponds to electrons is computer controlled via an optically isolated connection to the parallel printer port of the data collection computer. The process of computer switching is described in the last paragraph of this section. The SYNC INPUT is used to synchronize the timing of START (electron) pulses at the ortec 9353 card. Suppose for example, you take data as the diode laser frequency is swept over a 10 GHz range. The Toptica diode laser will produce a TTL sync pulse at the beginning of each scan. This sync pulse may be connected to the SYNC INPUT of the fast trigger box. In this way, the beginning of the scan can be communicated to the ORTEC 9353 and then to the data collection software. To see how this occurs, let’s look at the timing diagram for the fast sync box: The timing diagram above assumes that the switch is in the L/e position. If the switch is in the R/e position, switch the words right and left. A typical sync pulse input is shown in the first line. For laser spectroscopy, the Toptica laser produces a sync pulse that is high Z and really glitchy. For polarization modulation, the sync signal comes from our feedback stabilization box. The sync is not limited to these two cases. Any number of things can be scanned and correlated using the sync signal. Typically, the sync rep rate is between 1 and 100Hz. For slow scans (such as pressure tuning) the sync pulse is not used, but instead the scanworkcurrent.vi is used and data is taken in a stepped rather than scanned mode. For this case, the SYNC INPUT should be terminated. The stepped and scanned modes of data collection are described after the equipment section of this manual. Glitches in the sync pulse are removed by converting the first rising edge into a glitch free sync pulse of (I think) 10 microseconds in length. (second signal in the fast sync box timing diagram.) This implies a maximum rate of sync pulses of 100kHz. I am not positive of the deglitched pulse length. Someone should take out a scope and measure it at the test point in the schematic (pin 11 of U4). As soon as the sync signal is received, a 250ns disable signal is generated. A buffered copy of this signal is output at the front of the fast trigger box, but only for monitoring. It is NOT hooked up to anything other than a scope for observation. (Do NOT make the mistake of hooking it up to the ortec enable input.) When the disable signal is high, electron events signaled at the LEFT INPUT(for the L/e switch selection) are ignored. This prevents phase noise due to false sync signals. As soon as the sync signal is received, a 200ns TAG OUTPUT signal is created. This signal is buffered and output at the back of the fast sync box. This TAG OUTPUT should be connected to the TAG 1 input of the 9353 ortec card. (It might be TAG 0, I can’t for the life of me remember. Try it both ways only one will work.) The TAG signal lets the software controlling the ortec card know that the START (e) signal is not an ordinary electron, but instead is a sync signal. The e- and I+ outputs at the back of the fast sync box are 2.5 volt 100ns pulses that go into the START and STOP pulses of the ortec card. For the case the selector switch is in the L/e position, the left input is the stream of pulses produced by the 9327 preamp detecting electrons, along with the sync pulses that occur 50 ns after at the rising edge of sync input. The I+ output is the stream of pulses coming from the right detector. The STATUS OUTPUT is TTL high for the case that the left detector is switched to detect electrons, and TTL low for the case that the right detector is switched to detect electrons. A computer can be used to switch from L/e to R/e. To do this, the control switch should be in its center position. The computer control is designed to make the switch in the following way: (1) Using labview, pin three of the parallel printer port should be held at TTL high (for L/e) or low (for R/e). (2) When pin 3 is indicating the L/e or R/e state, pin 4 should be made to go through a TTL low to TTL high transition. This transition causes the box to change state. (3) After changing state of the fast sync box, Pin 4 should then be set low, and after a short delay, and pin 3 set low. (Pin 4 should be set low first so any glitches “reset” the box to the right state.) The state of the computer generated signals are both low while data is being collected in order to avoid any possible bias in the field reversal data. (4) The state of the box can be determined by placing a digital voltmeter on the STATUS OUT signal. Schematics of the fast sync box are given below: